This invention concerns a process for regenerating a catalyst at least partially deactivated after use in the treatment of a hydrocarbon charge containing at least one heteroelement from the sulfur, oxygen and nitrogen group and at least one metal from the vanadium, nickel and iron group, said deactivation resulting from the deposition of said metal on the catalyst initially formed of an inorganic carrier and at least one active metal or compound of active metal, selected from the group consisting of nickel, cobalt and molybdenum. Most often, the combinations nickel-molybdenum and cobalt molybdenum are particularly concerned.
This invention relates more particularly to the regeneration of catalysts used in the hydrotreatment and/or hydroconversion of crude oils and oil cuts of high boiling point, for example above 350.degree. C., such as straight-run or vacuum residues, shale oils, bituminous sand, as asphalt fraction or a fraction of liquid hydrocarbons obtained by coal liquefaction, straight-run or vacuum gas-oils or even fuel oils.
It may also be used as a basic process for the recovery of substantial metal amounts from catalysts used for treating heavy oil charges. For example, by treating 16,000 m.sup.3 /day of Orinoco oil, 7,000 tons of vanadium can be recovered.
During the operations of hydrotreatment (hydrodesulfurization, hydrodenitrogenation, hydrodemetallation), of hydrocracking or of catalytic cracking, the catalyst is progressively covered with deposits of coke and metals originating from the treated heavy charges.
Vanadium, nickel and iron are the three most important metals concerned but the invention is not limited to these three metals only.
The retention of metals and coke on the catalyst carrier results in a decrease of the pore volume and of the specific surface, thereby limiting the access of hydrocarbon molecules to the catalyst sites inside the catalyst particles. The catalyst activity thus decreases progressively or may be nullified when all the pores of the carrier are filled with vanadium, nickel and/or iron.
Many papers and patent applications have as their object the regeneration of catalysts poisoned by the above-mentioned metals.
In the known processes, hydrogen peroxide has often been used, either alone or as an aqueous solution, or combined with reducing washings or washings with diluted solutions of inorganic acids (nitric, sulfuric, hydrochloric acids), or associated with heteropolyacids or with basic salts as, for example, sodium carbonate.
On the other hand, vanadium and nickel extractions by aqueous solutions of hydrogen peroxide have been generally performed from these metals in the state of sulfides or directly on used and/or exhausted catalysts, or after a presulfurization with various sulfurizing agents, mostly with hydrogen sulfide, when the used catalysts do not contain a sufficient amount of sulfur.
According to the usual explanation, this presulfurization causes the metals to migrate to the surface of the catalyst particle. Vanadium and nickel extraction is accordingly easier.
U.S. Pat. No. 3,562,150 discloses vanadium extraction from thermodynamically stable vanadium sulfides (V.sub.2 S.sub.3, V.sub.2 S.sub.5). This patent establishes the fact that, in order to obtain the best results, vanadium extraction from the used catalysts by hydrogen peroxide solutions must be performed before the roasting step in the presence of air at 510.degree. C., for 16 hours. When reversing the order of these two treatments, the metal extraction and the activity of the regenerated catalyst are not as good.
The commercial processes for demetallation of used catalysts, e.g., the SINCLAIR DEMET PROCESS, published in "The Oil and Gas Journal" of Aug. 27, 1962, pages 92-96 and in the article entitled "The demetallization of cracking catalysts" published in I & EC Product Research and Development, Volume 2, pages 238-332, December 1963, or in "Hydrocarbon Processing & Petroleum Refiner", volume 41, no. 7, July 1962, indicates that metals extraction by hydrogen peroxide aqueous solutions must be preceded by a presulfurization step with hydrogen sulfide.
U.S. Pat. No. 4,101,444 indicates that metal extraction by means of hydrogen peroxide must be preceded by a washing treatment with a reducing agent consisting of sulfur dioxide dissolved in water.
Finally, U.S. Pat. No. 4,268,415 states that metal extraction is directly performed from metal sulfides of used catalysts after washing with organic solvents and/or must be preceded by a previous sulfurization with hydrogen sulfide when the catalyst to be treated has an insufficient sulfur content. This patent shows that the addition of a suitable amount of hydrogen peroxide clearly improves the metal extraction by heteropolyacids.
The applicant's work has shown that the known processes suffer from many disadvantages:
substantial etching of the catalyst carrier, when the latter contains alumina or silica-alumina or a zeolite, by the sulfuric acid formed during the extraction of the metals in the sulfide state or by steam and nitric acid extraction U.S. Pat. No. 4,501,820 PA0 substantial decomposition of hydrogen peroxide to water and oxygen gas, in contact with inorganic catalyst carriers and by the extracted metal ions, making the process rather uneconomical, PA0 reactivation only to an insufficient extent, resulting apparently from an insufficient removal of the undesirable metals. PA0 (a) The catalyst is roasted in the presence of an oxygen-containing gas so as to remove at least 90% of the sulfur, PA0 (b) the catalyst obtained in step (a) is contacted with a hydrogen peroxide aqueous solution containing at least one organic compound comprising at least one acidic functional group so as to remove at least 10% of the deposited vanadium, nickel or iron metals, and PA0 (c) the regenerated catalyst is separated from the aqueous solution of metal ions.